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bpo-39534: Doc: Clarify return in finally (GH-18324)
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JulienPalard committed Feb 6, 2020
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36 changes: 27 additions & 9 deletions Doc/tutorial/errors.rst
Expand Up @@ -388,15 +388,33 @@ example::
File "<stdin>", line 2, in <module>
KeyboardInterrupt

If a :keyword:`finally` clause is present, the :keyword:`finally` clause will execute as the last task before the :keyword:`try` statement completes. The :keyword:`finally` clause runs whether or not the :keyword:`try` statement produces an exception. The following points discuss more complex cases when an exception occurs:

* If an exception occurs during execution of the :keyword:`!try` clause, the exception may be handled by an :keyword:`except` clause. If the exception is not handled by an :keyword:`except` clause, the exception is re-raised after the :keyword:`!finally` clause has been executed.

* An exception could occur during execution of an :keyword:`!except` or :keyword:`!else` clause. Again, the exception is re-raised after the :keyword:`!finally` clause has been executed.

* If the :keyword:`!try` statement reaches a :keyword:`break`, :keyword:`continue` or :keyword:`return` statement, the :keyword:`finally` clause will execute just prior to the :keyword:`break`, :keyword:`continue` or :keyword:`return` statement's execution.

* If a :keyword:`finally` clause includes a :keyword:`return` statement, the :keyword:`finally` clause's :keyword:`return` statement will execute before, and instead of, the :keyword:`return` statement in a :keyword:`try` clause.
If a :keyword:`finally` clause is present, the :keyword:`!finally`
clause will execute as the last task before the :keyword:`try`
statement completes. The :keyword:`!finally` clause runs whether or
not the :keyword:`!try` statement produces an exception. The following
points discuss more complex cases when an exception occurs:

* If an exception occurs during execution of the :keyword:`!try`
clause, the exception may be handled by an :keyword:`except`
clause. If the exception is not handled by an :keyword:`!except`
clause, the exception is re-raised after the :keyword:`!finally`
clause has been executed.

* An exception could occur during execution of an :keyword:`!except`
or :keyword:`!else` clause. Again, the exception is re-raised after
the :keyword:`!finally` clause has been executed.

* If the :keyword:`!try` statement reaches a :keyword:`break`,
:keyword:`continue` or :keyword:`return` statement, the
:keyword:`!finally` clause will execute just prior to the
:keyword:`!break`, :keyword:`!continue` or :keyword:`!return`
statement's execution.

* If a :keyword:`!finally` clause includes a :keyword:`!return`
statement, the returned value will be the one from the
:keyword:`!finally` clause's :keyword:`!return` statement, not the
value from the :keyword:`!try` clause's :keyword:`!return`
statement.

For example::

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